Running Shoes

ABSTRACT

A running shoe comprises an upper and a midsole attached to the upper, the midsole having a front portion corresponding to a forefoot and a rear portion corresponding to a heel. The front portion of the midsole may define a toe spring of at least 40 mm and a plurality of flex grooves, the plurality of flex grooves including one or more horizontal flex grooves and one or more longitudinal flex grooves, the horizontal flex groove(s) extending in a lateral to medial direction of the running shoe and allowing the front portion of the midsole to lie flat in response to application of less than 15 pounds of force against the toe spring, the longitudinal flex groove(s) extending in a front to back direction of the running shoe. The rear portion of the midsole may have a flat bottom that is narrower than the upper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims the benefit of U.S. Provisional Application No. 63/295,628, filed Dec. 31, 2021 and entitled “RUNNING SHOES,” the entire disclosure of which is expressly incorporated by reference herein.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

When running or walking barefoot on natural, earthen surfaces, the foot does some unique things that it does not as readily do when shod. Toes lift 20-40 degrees and metatarsal heads drop slightly in the swing phase of the gait cycle. The body's center of mass travels from the heel to the forefoot largely unimpeded and more quickly than when in a shoe. The forefoot also expands up to 20%, mostly laterally, as it becomes weighted upon contact with the ground. Unfortunately, the biomechanics of running and walking barefoot on earthen surfaces are largely overlooked in the design of running shoes, which must be cushioned for use on hard, flat, manmade surfaces like concrete and pavement. By inhibiting the natural functions of the foot, available running shoes limit the foot's performance and may even increase the risk of injury.

BRIEF SUMMARY

The present disclosure contemplates footwear for overcoming the above drawbacks associated with the related art. One aspect of the embodiments of the present disclosure is a running shoe comprising an upper and a midsole attached to the upper. The midsole may have a front portion corresponding to a forefoot and a rear portion corresponding to a heel. The front portion of the midsole may define a toe spring of at least 40 mm and a plurality of flex grooves. The plurality of flex grooves may include one or more horizontal flex grooves and one or more longitudinal flex grooves, the one or more horizontal flex grooves extending in a lateral to medial direction of the running shoe and allowing the front portion of the midsole to lie flat in response to application of less than 15 pounds of force against the toe spring, the one or more longitudinal flex grooves extending in a front to back direction of the running shoe. The rear portion of the midsole may have a flat bottom that is narrower than the upper in the lateral to medial direction of the running shoe.

The toe spring may be at least 50 mm. The one or more horizontal flex grooves may allow the front portion of the midsole to lie flat in response to application of less than 10 pounds of force against the toe spring, preferably less than 5 pounds of force. The one or more horizontal flex grooves may include a first lower flex groove extending into the front portion of the midsole from a bottom thereof and a first upper flex groove extending into the front portion of the midsole from a top thereof, the first upper flex groove being vertically aligned with the first lower flex groove so as to reduce a thickness of the midsole therebetween (e.g., to 20%-35% of a maximum thickness of the midsole, preferably 25%-30%). The one or more horizontal flex grooves may include a first flex groove and a second flex groove spaced from each other in the front to back direction of the running shoe. The one or more longitudinal flex grooves may include a first lower flex groove extending into the front portion of the midsole from a bottom thereof and a first upper flex groove extending into the front portion of the midsole from a top thereof, the first upper flex groove being vertically aligned with the first lower flex groove so as to reduce a thickness of the midsole therebetween (e.g., to 20%-35% of a maximum thickness of the midsole, preferably 25%-30%). The one or more longitudinal flex grooves may include a first flex groove and a second flex groove spaced from each other in the lateral to medial direction of the running shoe. The upper may comprise an elastic material.

The rear portion of the midsole may be rounded from the flat bottom thereof to the lateral and medial sides of the running shoe (e.g., according to one or more radii of curvature of 15-25 mm). The flat bottom of the rear portion of the midsole may be rounded about a perimeter thereof.

The midsole may exhibit zero drop from the rear portion to the front portion thereof. A maximum width of the front portion of the midsole in the lateral to medial direction of the running shoe may be greater than 140% of a maximum width of the rear portion of the midsole in the lateral to medial direction of the running shoe.

The running shoe may comprise an outsole attached to the midsole.

Another aspect of the embodiments of the present disclosure is a running shoe comprising an upper and a sole unit attached to the upper. The sole unit may have a front portion corresponding to a forefoot and a rear portion corresponding to a heel. The front portion of the sole unit may define a toe spring of at least 40 mm and a plurality of flex grooves. The plurality of flex grooves may include one or more horizontal flex grooves and one or more longitudinal flex grooves, the one or more horizontal flex grooves extending in a lateral to medial direction of the running shoe and allowing the front portion of the sole unit to lie flat in response to application of less than 15 pounds of force against the toe spring, the one or more longitudinal flex grooves extending in a front to back direction of the running shoe. The rear portion of the sole unit may have a flat bottom that is narrower than the upper in the lateral to medial direction of the running shoe.

The toe spring may be at least 50 mm. The one or more horizontal flex grooves may allow the front portion of the sole unit to lie flat in response to application of less than 10 pounds of force against the toe spring, preferably less than 5 pounds of force. The one or more horizontal flex grooves may include a first lower flex groove extending into the front portion of the sole unit from a bottom thereof and a first upper flex groove extending into the front portion of the sole unit from a top thereof, the first upper flex groove being vertically aligned with the first lower flex groove so as to reduce a thickness of the sole unit therebetween (e.g., to 20%-35% of a maximum thickness of the sole unit, preferably 25%-30%). The one or more horizontal flex grooves may include a first flex groove and a second flex groove spaced from each other in the front to back direction of the running shoe. The one or more longitudinal flex grooves may include a first lower flex groove extending into the front portion of the sole unit from a bottom thereof and a first upper flex groove extending into the front portion of the sole unit from a top thereof, the first upper flex groove being vertically aligned with the first lower flex groove so as to reduce a thickness of the sole unit therebetween (e.g., to 20%-35% of a maximum thickness of the sole unit, preferably 25%-30%). The one or more longitudinal flex grooves may include a first flex groove and a second flex groove spaced from each other in the lateral to medial direction of the running shoe. The upper may comprise an elastic material.

The rear portion of the sole unit may be rounded from the flat bottom thereof to the lateral and medial sides of the running shoe (e.g., according to one or more radii of curvature of 15-25 mm). The flat bottom of the rear portion of the sole unit may be rounded about a perimeter thereof.

The sole unit may exhibit zero drop from the rear portion to the front portion thereof. A maximum width of the front portion of the sole unit in the lateral to medial direction of the running shoe may be greater than 140% of a maximum width of the rear portion of the sole unit in the lateral to medial direction of the running shoe.

The sole unit may comprise a midsole and an outsole.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:

FIG. 1 is a right side view of a running shoe for a right foot, showing a lateral (outer) side thereof;

FIG. 2 is a left side view of the running shoe, showing a medial (inner) side thereof;

FIG. 3 is another ride side view of the running shoe with the front of the shoe flexed downward;

FIG. 4 is a bottom view of the running shoe;

FIG. 5 is a top view of a midsole of the shoe;

FIG. 6 is a cross-sectional view taken along the line 6-6 in FIG. 5 ;

FIG. 7 is a cross-sectional view taken along the line 7-7 in FIG. 5 ; and

FIG. 8 is a cross-sectional view taken along the line 8-8 in FIG. 5 .

DETAILED DESCRIPTION

The present disclosure encompasses various embodiments of footwear and, in particular, running shoes. The detailed description set forth below in connection with the appended drawings is intended as a description of several currently contemplated embodiments and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.

FIGS. 1-8 are views of a running shoe 100 for a right foot. While not separately illustrated, the running shoe 100 may also be symmetrically designed for a left foot. The resulting pair of running shoes 100 may be worn for running or walking on ordinary running surfaces, including roads and sidewalks, while advantageously allowing and encouraging the biomechanics and sensations of running or walking barefoot on natural, earthen surfaces, thus enhancing performance and reducing the risk of injury. The running shoe 100 may generally include an upper 110 (e.g., vamp, quarter, etc.) and a sole unit, with the sole unit typically comprising a midsole 120 and an outsole 130. The midsole 120 may be attached to the upper 110 and provide cushioning to absorb the shock of running on hard surfaces and may be made of ethylene vinyl acetate (EVA), for example, while the outsole 130 may be a thinner, rubber portion of the sole unit that may be attached to the bottom of the midsole 120 and patterned to provide traction. Advantageously, the sole unit, and particularly the midsole 120, may be uniquely designed both in a front portion 122 and a rear portion 124 thereof (see FIGS. 3 and 4 ) to promote the natural barefoot action of the wearer's foot without sacrificing the protective cushioning of the running shoe 100.

Referring to FIGS. 1-3 , the front portion 122 of the midsole 120, corresponding to a forefoot of the wearer, may define a toe spring H (see FIG. 3 ) that is great enough to allow and encourage the toes' natural vertical extension of 20-40 degrees relative to the rest of the foot during the swing phase of the gait cycle. (The relaxed “toe-up” position is shown with broken lines in FIG. 3 .) For a standard U.S. men's size 9D, for example, the toe spring H may be 40 mm or more (e.g., 40-60 mm), preferably at least 50 mm (e.g., 55 mm), as measured vertically from the ground to the foremost point 123 on the bottom of the shoe 100 (i.e., the farthest forward point that contacts the ground). For other shoe sizes, the toe spring H, as well as any other absolute measurements (e.g., millimeter measurements) described herein, may be proportionally greater or less according to conventional shoe sizing algorithms. It is also contemplated that the toe spring H may be described as an angle of elevation to the foremost point 123 (while the shoe 100 is in the relaxed “toe-up” position) as observed from the farthest forward point on the shoe 100 that contacts the ground during the “toe-up” position (indicated with reference number 125 in FIG. 3 ), which may be 25-40 degrees, for example. Unlike the rigid toe spring features of conventional running shoes, the front portion 122 of the midsole 120 may be flexible enough to be made to lie flat as shown in FIG. 3 easily and without substantial effort, such that the weight of the wearer's foot while running may naturally produce the flexed downward state shown in FIG. 3 during each stride. In this regard, the front portion 122 of the midsole 120 may be made to lie flat in response to application of less than 15 pounds of force against the toe spring H (e.g., normal to the top of the midsole 120 or sockliner), preferably less than 10 pounds of force or even less than 5 pounds of force.

The midsole 120 may preferably exhibit zero mm of drop from the rear portion 124 to the front portion 122 thereof while the running shoe 100 is worn flat against the ground (with the toes lying flat as described above), where drop may refer to the difference in height of the midsole between the rear of the foot and the ball of the foot. Preferably, the midsole 120 may exhibit zero drop from the rear portion 124 all the way to the foremost point 123 described above, rather than merely to the ball of the wearer's foot, where drop is typically measured to, for example. As a result, the toes, when the shoe sits or becomes weighted in the toes-flattened position, are able to exert pressure against a solid surface and initiate additional stabilization of the foot sooner in the gait cycle and when standing, just as the foot would if barefoot and not in a shoe. In the case of a conventional, cushioned shoe (where the cushioning is comprised of a midsole height greater than 10-15 mm and where that height tapers from near the ball of the foot to the tip of the shoe), the toes are unable to exert pressure against a solid surface until the very end of the foot's ground contact time, when the foot rolls over the toes and it is too late to initiate significant additional stabilization forces through the toes. The unique combination of previously described forefoot flexibility, combined with a significantly cushioned midsole of at least 10-15 mm of height and possessing zero drop as measured from the heal to the tips of the toes, may allow the shod foot to operate as effectively on concrete and pavement as the bare foot would on earthen surfaces.

Flexibility of the front portion 122 of the midsole 120 may be achieved, at least in part, by the inclusion therein of a plurality of flex grooves 126 a, 126 b, 127 a, 127 b (see FIGS. 4-7 ). In particular, one or more horizontal flex grooves 126 a, 126 b may provide the flexibility to allow the front portion 122 of the midsole 120 to easily lie flat as shown in FIG. 3 . The one or more horizontal flex grooves 126 a, 126 b may span the width of the midsole 120 in the front portion 122 thereof. Referring to FIGS. 4-6 , the one or more horizontal flex grooves 126 a, 126 b may include a first lower flex groove 126 a-1 extending into the front portion 122 of the midsole 120 from a bottom thereof and a first upper flex groove 126 a-2 extending into the front portion of the midsole from a top thereof, with the first upper flex groove 126 a-2 being vertically aligned with the first lower flex groove 126 a-1 so as to reduce a thickness of the midsole 120 therebetween (and thus promote flexibility near the base of the wearer's toes). The thickness of the midsole 120 may be reduced in this way to 20%-35% (preferably 25%-30%) of a maximum thickness of the midsole 120, for example. The reduced thickness may be 4-10 mm, for example, which may provide sufficient flexibility while still having enough structural integrity to be reliably formed by a conventional molding process and to not tear under normal walking and running conditions. Additional flexibility, and in particular a liveliness or springiness of the action of moving the front portion 122 of the midsole 120 between the two positions shown in FIG. 3 , may be provided by the material of the upper 110, which may be stretched over the midsole 120 and have built-in elasticity. In this regard, the upper 110 may comprise an elastic material such as a stretch knit fiber or one or more elasticated bungees sewn or otherwise affixed or embedded therein and attached to the midsole 120.

The one or more horizontal flex grooves 126 a, 126 b may include one or more horizontal flex grooves 126 a, 126 b spaced from each other in a front to back direction of the running shoe 100 (e.g., in a direction from the front 102 to the back 104 of the running shoe 100). In the illustrated example, two first horizontal flex grooves 126 a-1, 126 a-2 (lower and upper, respectively) promote flexibility near the base of the wearer's toes as described above, while two second horizontal flex grooves 126 b-1, 126 b-2 (lower and upper, respectively) are spaced therefrom so as to be farther back near the rearmost end of the front portion 122 of the midsole 120. These second horizontal flex grooves 126 b may similarly reduce the thickness of the midsole 120 therebetween (e.g., to 20%-35%, preferably 25%-30%, or 4-10 mm, for example) to promote flexibility of the midsole 120. The placement of the second horizontal flex grooves 126 b may, in addition to in some cases further improving the flexibility of the toe spring as described above, make it easier for the wearer to lift the rear portion 124 of the midsole 120 while the front portion 122 of the midsole 120 is still planted on the ground as the wearer pushes off the ground with each stride.

In addition to the one or more horizontal flex grooves 126 a, 126 b, the front portion 122 of the midsole 120 may further define one or more longitudinal flex grooves 127 a, 127 b that extend in the front to back direction of the running shoe 100 (see FIGS. 4, 5, and 7 ). The one or more longitudinal flex grooves 127 a, 127 b may span the length of the front portion 122 of the midsole 120 (e.g., from the front 102 of the shoe to the rearmost end of the front portion 122, typically between one-third and one-half of the way from the front 102 to the back 104 of the shoe 100). The one or more longitudinal flex grooves 127 a, 127 b may provide flexibility to allow the front portion 122 of the midsole 120 to bend independently at different locations in a lateral to medial direction of the running shoe 100 (e.g., in a direction from the lateral side 106 to the medial side 108 of the running shoe 100). In this way, the running shoe 100 may allow and encourage the natural biomechanics of the wearer's foot as 4th and 5th metatarsal heads drop earlier than the others during the wearer's stride and/or as 2nd and 3rd metatarsal heads drop earlier than the 1st metatarsal head.

The one or more longitudinal flex grooves 127 a, 127 b may include a first lower flex groove 127 a-1 extending into the front portion 122 of the midsole 120 from a bottom thereof and a first upper flex groove 127 a-2 extending into the front portion of the midsole from a top thereof, with the first upper flex groove 127 a-2 being vertically aligned with the first lower flex groove 127 a-1 so as to reduce a thickness of the midsole 120 therebetween (and thus promote flexibility between the wearer's 4th and 5th toes and the rest of the wearer's toes). The one or more longitudinal flex grooves 127 a, 127 b may further include, spaced apart from the first flex groove(s) 127 a-1, 127 a-2 in the lateral to medial direction of the running shoe 100, a second lower flex groove 127 b-1 extending into the front portion 122 of the midsole 120 from a bottom thereof and a second upper flex groove 127 b-2 extending into the front portion of the midsole from a top thereof, with the second upper flex groove 127 b-2 being vertically aligned with the second lower flex groove 127 b-1 so as to reduce a thickness of the midsole 120 therebetween (and thus promote flexibility between the wearer's big toe and the rest of the wearer's toes). The thickness of the midsole 120 may be reduced in this way to 20%-35% (preferably 25%-30% or 4-10 mm, for example) of a maximum thickness of the midsole 120, for example. The use of first and second longitudinal flex grooves 127 a, 127 b spaced apart in this way may effectively segment the front portion 122 of the midsole 120 into forefoot pods or segments, one supporting the 1st ray, one supporting the 2nd and 3rd rays, and one supporting the 4th and 5th rays. The longitudinal flex grooves 127 a, 127 b may allow each of the pods to move independent of one another, for example, by 2-10 mm vertically.

Owing to the combined toe spring and flexibility of the front portion 122 of the midsole 120, the disclosed running shoe 100 may allow the wearer's toes first to lift during the swing phase of the gait cycle according to the toes-up bias imparted by the toe spring (i.e., the “toe-up” position shown with broken lines in FIG. 3 ), pre-tensioning the musculature of the foot prior to impact with the ground, and then to lower in two or more distinct, accordion-like movements. When barefoot, the toes naturally do this in five distinct accordion-like movements (one per toe). By grouping the toes as described above using first and second longitudinal flex grooves 127 a, 127 b spaced apart from each other, the toes may lower in three movements, first the 4th and 5th toes, then the 2nd and 3rd toes, and last the 1st (big) toe, resulting in a similar effect that closely mirrors the natural biomechanics of the foot while running or walking barefoot. It is contemplated, however, that more (four or five) or fewer (two) groupings may be used. The disclosed running shoe 100 may advantageously make such individual movements of the toes possible within the confines of a cushioned shoe having a midsole 120 that cushions and supports the wearer's foot including the toes (unlike, for example, Vibram FiveFingers, sold by Vibram Corporation). Moreover, this may have the effect of creating distinct impact zones, much like the crumple zones in a car, each absorbing impact force separately without transferring it as quickly or directly to the other segments over a slightly lengthened period of time, thus dampening direct impact forces by spreading them out over a greater distance and period of time.

Preferably, a maximum width of the front portion 122 of the midsole 120 in the lateral to medial direction of the running shoe 100 may be large enough to allow the wearer's forefoot to freely splay or spread more than 10% (e.g., 15-20%) within the shoe, which the foot is designed to do while barefoot. For example, the maximum width of the front portion 122 may be greater than 140% (preferably greater than 150%) of a maximum width of the rear portion 124 of the midsole 120 in the lateral to medial direction of the running shoe 100. The maximum width of the front portion 122 may be, for example greater than 90 mm, preferably 100-110 mm, for a standard U.S. men's size 9D (with proportionally greater or less width for other sizes as noted above). The width of the midsole 120 may be measured at the top of the midsole 120, for example. By allowing the foot to splay unimpeded within the shoe 100 in one plane and due to the toes lowering in another direction toward the plane over a slightly longer period of time, the impact forces may be further dampened, further reducing the risk of injury and making for a more cushioned footstrike.

Referring now to FIGS. 4, 6, and 8 , the rear portion 124 of the midsole 120, corresponding to the heel of the wearer, may have a flat bottom 128 that is narrower than the upper 110 in the lateral to medial direction of the running shoe 100. As shown in FIG. 8 , which is a cross-sectional view taken along the line 8-8 in FIG. 5 , a width W_(B) of the flat bottom 128 may be less than a width W_(U) of the upper 110. For a standard U.S. men's size 9D, for example, the width W_(B) of the flat bottom 128 may be less than 65 mm at its widest (preferably less than 50 mm, with the corresponding width W_(U) of the upper 110 being greater than 60 mm), and with proportionally greater or smaller measurements being used for other sizes as explained above. As a result of W_(B) being less than W_(U), the flat bottom 128 may fall substantially underneath the wearer's heel, unlike conventional running shoes whose midsoles typically have a very wide rear portion that extends laterally and medially beyond the upper and thus beyond the actual heel of the wearer. Preferably, the flat bottom 128 may extend only so far as the actual flattened area of contact between the wearer's naturally round heel and the top of the midsole 120 or sockliner within the running shoe 100, effectively simulating the flattened area of contact that would occur were the naturally round heel of the wearer to press down on the ground directly.

The relationship W_(B)<W_(U) may be met along the entire flat bottom 128 of the rear portion 124 of the running shoe 100 at any given longitudinal position (i.e., in the front to back direction of the running shoe 100). The flat bottom 128 of the rear portion 124 may be rounded about a perimeter thereof as shown in FIG. 4 . For example, the rear portion 124 of the midsole 120 may be rounded from the lateral side 106 to the medial side 108 of the running shoe 100 around the back 104 thereof, and the perimeter of the flat bottom 128 may trace a corresponding curve therewithin. Toward the foremost part of the rear portion 124 of the midsole 120 (which may end about one-third of the way from the back 104 to the front 102 of the running shoe 100), the perimeter of the flat bottom 128 may close such that the flat bottom 128 takes on an egg shape as shown or other ovoid form, which may preferably correspond to the shape of the wearer's flattened heel within the shoe 100. Alternatively, the flat bottom 128 of the rear portion 124 of the midsole 120 may not end in the rear portion 124 as shown in FIG. 4 and may instead continue forward underneath the midfoot of the wearer, with the midsole 120 thus defining a connecting bridge that extends from the rear portion 124 to the front portion 122.

Referring again to FIG. 8 , the rear portion 124 of the midsole 120 may be rounded from the flat bottom 128 thereof to the lateral and medial sides 106, 108 of the running shoe 100 according to one or more radii of curvature R1, R2, which may be in the range of 15-25 mm, for example. It is contemplated that the lateral radius of curvature R1 may be the same as or different from the medial radius of curvature R2 at any given longitudinal position. The rear portion 124 of the midsole 120 may likewise be rounded from the flat bottom 128 thereof to the back 104 of the running shoe 100 according to a radius of curvature R3 (see FIG. 6 ), which may be the same as or different from either or both of the radii of curvature R1, R2. By defining such a substantial rounding between the flat bottom 128 and the sides 106, 108 and/or back 104 of the running shoe 100, the rear portion 124 of the disclosed midsole 120 (with optional outsole 130) may approximate the rounding of a person's heel.

Owing to the flat bottom 128 of the rear portion 124 of the midsole 120 being narrower than the upper 110, as well as the preferably substantial rounding between the flat bottom 128 and the sides 106, 108 and/or back 104 of the running shoe 100, the contact between the running shoe 100 and the ground may simulate the contact between a bare heel and the ground. This may result in various advantages, which may include a faster and smoother transition of impact forces and the body's center of mass from heel to forefoot through the ground contact phase of the gait cycle and/or reduced rotational torque applied to the foot and transferred to other lower limb joints from naturally occurring pronation (as opposed to the acceleration of naturally occurring pronation and torque forces from shoes with wider, significantly larger flat heel surfaces). The more efficient transfer of impact forces and the body's center of mass from heel to forefoot, coupled with the reduced rotational forces of the foot, may mitigate the forces created by running and walking, reducing the risk of injury in comparison with using conventional running shoes.

In combination, the unique design features of both the front portion 122 and the rear portion 124 of the midsole 120 described above may work together in concert to create a benefit of reduced impact and torque forces that is greater than the sum of each if accounted for independent of one another. The features of the front portion 122 may feed the features of the rear portion 124 and vice versa in successively greater step-downs of impact forces and torque, resulting in a composite reduction of forces that cannot be otherwise achieved.

Throughout the above disclosure, various example measurements are provided for a U.S. men's size 9D with the explanation that the measurements may be greater or less according to conventional shoe sizing algorithms. By way of further example, the following Table 1 shows selected last measurements of a last that may be used to produce the disclosed running shoe 100. The Size column reflects standard U.S. men's shoe sizes, while all other measurements are in millimeters.

TABLE 1 Stick Bottom Bottom LBP Heel Toe Size Length Length Width Width Spring 3.5 221.16 232.74 94.6 53.8 47.7 4 225.39 236.97 95.6 54.4 48.4 4.5 229.62 241.20 96.7 55.0 49.0 5 233.85 245.43 97.7 55.6 49.7 5.5 238.08 249.66 98.8 56.2 50.4 6 242.31 253.89 99.9 56.8 51.0 6.5 246.54 258.12 100.9 57.5 51.7 7 250.77 262.35 102.0 58.1 52.4 7.5 255.00 266.58 103.0 58.7 53.0 8 259.23 270.81 104.1 59.3 53.7 8.5 263.46 275.04 105.2 59.9 54.3 9 267.69 279.27 106.2 60.5 55.0 9.5 271.92 283.50 107.3 61.1 55.7 10 276.15 287.73 108.3 61.7 56.3 10.5 280.38 291.96 109.4 62.3 57.0 11 284.61 296.19 110.5 62.9 57.6 11.5 288.84 300.42 111.5 63.5 58.3 12 293.07 304.65 112.6 64.1 59.0 12.5 297.30 308.88 113.6 64.7 59.6 13 310.53 313.11 114.7 65.3 60.3 13.5 305.76 317.34 115.8 65.9 61.0 14 309.99 321.57 116.8 66.5 61.6 14.5 314.22 325.80 117.9 67.1 62.3 15 318.45 330.03 118.9 67.7 62.9 15.5 322.68 334.26 120.0 68.3 63.6 16 326.91 338.49 121.1 68.9 64.3 16.5 331.14 342.72 122.1 69.5 64.9 17 335.37 346.95 123.2 70.1 65.6 17.5 339.60 351.18 124.2 70.7 66.2 18 343.83 355.41 125.3 71.3 66.9

As noted above, the midsole 120 of the running shoe 100 may exhibit zero drop from the rear portion 124 all the way to the foremost point 123 described above. As such, the midsole 120 may have a consistent thickness instead of tapering in the region of the wearer's toes. As a result, the toe spring measurements of the last, as exemplified in Table 1, may match the toe spring measurements of the finishing running shoe 100 that includes the midsole 120. Accordingly, another aspect of the embodiments of the present disclosure is a last for manufacturing a running shoe, the last defining a toe spring of at least 40 mm, preferably at least 50 mm. The last may be used to produce the upper 110, with the disclosed midsole 120, outsole 130, etc. being attached thereto to the produce a running shoe 100 as described herein.

The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments. 

What is claimed is:
 1. A running shoe comprising: an upper; and a midsole attached to the upper, the midsole having a front portion corresponding to a forefoot and a rear portion corresponding to a heel, the front portion of the midsole defining a toe spring of at least 40 mm and a plurality of flex grooves, the plurality of flex grooves including one or more horizontal flex grooves and one or more longitudinal flex grooves, the one or more horizontal flex grooves extending in a lateral to medial direction of the running shoe and allowing the front portion of the midsole to lie flat in response to application of less than 15 pounds of force against the toe spring, the one or more longitudinal flex grooves extending in a front to back direction of the running shoe, the rear portion of the midsole having a flat bottom that is narrower than the upper in the lateral to medial direction of the running shoe.
 2. The running shoe of claim 1, wherein the toe spring is at least 50 mm.
 3. The running shoe of claim 1, wherein the one or more horizontal flex grooves allow the front portion of the midsole to lie flat in response to application of less than 10 pounds of force against the toe spring.
 4. The running shoe of claim 3, wherein the one or more horizontal flex grooves allow the front portion of the midsole to lie flat in response to application of less than 5 pounds of force against the toe spring.
 5. The running shoe of claim 1, wherein the one or more horizontal flex grooves includes a first lower flex groove extending into the front portion of the midsole from a bottom thereof and a first upper flex groove extending into the front portion of the midsole from a top thereof, the first upper flex groove being vertically aligned with the first lower flex groove so as to reduce a thickness of the midsole therebetween.
 6. The running shoe of claim 5, wherein the first upper flex groove is vertically aligned with the first lower flex groove so as to reduce the thickness of the midsole therebetween to 20%-35% of a maximum thickness of the midsole.
 7. The running shoe of claim 6, wherein the first upper flex groove is vertically aligned with the first lower flex groove so as to reduce the thickness of the midsole therebetween to 25%-30% of a maximum thickness of the midsole.
 8. The running shoe of claim 1, wherein the one or more horizontal flex grooves includes a first flex groove and a second flex groove spaced from each other in the front to back direction of the running shoe.
 9. The running shoe of claim 1, wherein the one or more longitudinal flex grooves includes a first lower flex groove extending into the front portion of the midsole from a bottom thereof and a first upper flex groove extending into the front portion of the midsole from a top thereof, the first upper flex groove being vertically aligned with the first lower flex groove so as to reduce a thickness of the midsole therebetween.
 10. The running shoe of claim 9, wherein the first upper flex groove is vertically aligned with the first lower flex groove so as to reduce the thickness of the midsole therebetween to 20%-35% of a maximum thickness of the midsole.
 11. The running shoe of claim 10, wherein the first upper flex groove is vertically aligned with the first lower flex groove so as to reduce the thickness of the midsole therebetween to 25%-30% of a maximum thickness of the midsole.
 12. The running shoe of claim 1, wherein the one or more longitudinal flex grooves includes a first flex groove and a second flex groove spaced from each other in the lateral to medial direction of the running shoe.
 13. The running shoe of claim 1, wherein the upper comprises an elastic material.
 14. The running shoe of claim 1, wherein the rear portion of the midsole is rounded from the flat bottom thereof to the lateral and medial sides of the running shoe according to one or more radii of curvature of 15-25 mm.
 15. The running shoe of claim 1, wherein the flat bottom of the rear portion of the midsole is rounded about a perimeter thereof.
 16. The running shoe of claim 1, wherein the midsole exhibits zero drop from the rear portion to the front portion thereof.
 17. The running shoe of claim 1, wherein a maximum width of the front portion of the midsole in the lateral to medial direction of the running shoe is greater than 140% of a maximum width of the rear portion of the midsole in the lateral to medial direction of the running shoe.
 18. The running shoe of claim 1, further comprising an outsole attached to the midsole.
 19. A running shoe comprising: an upper; and a sole unit attached to the upper, the sole unit having a front portion corresponding to a forefoot and a rear portion corresponding to a heel, the front portion of the sole unit defining a toe spring of at least 40 mm and a plurality of flex grooves, the plurality of flex grooves including one or more horizontal flex grooves and one or more longitudinal flex grooves, the one or more horizontal flex grooves extending in a lateral to medial direction of the running shoe and allowing the front portion of the sole unit to lie flat in response to application of 2-15 pounds of force against the toe spring, the one or more longitudinal flex grooves extending in a front to back direction of the running shoe, the rear portion of the sole unit having a flat bottom that is narrower than the upper in the lateral to medial direction of the running shoe.
 20. The running shoe of claim 16, wherein the sole unit comprises a midsole and an outsole. 